Gaseous hydrides such as arsine, phosphine, hydrogen selenide, silane and diborane are important as a raw material for producing a compound semiconductor such as gallium-arsenic (GaAs) or gallium-phosphorus (GaP) as an ion implantation gas, and the amount thereof used is increasing year by year. At the same time, with the increase of the integration extent of a semiconductor device, gaseous hydrides having an extremely low content of impurities have been required.
Gaseous hydrides for use in the production of semiconductors are generally commercially available as the gaseous hydride itself or in the form of being diluted with hydrogen gas or an inert gas.
These gaseous hydrides contain oxygen and moisture as impurities and of these impurities, moisture can be removed by a dehumidifying agent such a synthetic zeolite.
The oxygen content in commercially available gaseous hydrides is usually 10 ppm or less, but, recently, gaseous hydrides contained in a bomb having a relatively low oxygen content of from 0.1 to 0.5 ppm are commercially available.
There are almost no methods for efficiently removing oxygen contained in gaseous hydrides but a method for purifying arsine by bringing a material having an adsorptive power to arsine, such as active carbon or a synthetic zeolite, into contact with arsine to reduce the oxygen content to 1 ppm or less is proposed in, for example, JP-A-62-78116 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application").
However, gaseous hydrides having an oxygen content to an extent of slightly below 1 ppm cannot sufficiently meet the requirement in a recent semiconductor production process and it has strongly been desired to reduce the oxygen content in gaseous hydrides to 0.1 ppm or less.
Further, since such gaseous hydrides are sometimes contaminated by the entrance of impurities such as air in supplying steps to an apparatus for producing semiconductors such as a step of connecting a gaseous hydride bomb to the apparatus or a step of changing pipes, it is desired to finally remove impurities immediately before the apparatus.